SAW devices, such as delay lines and resonators, are known for measuring acceleration, stress, strain, temperature, pressure, and/or other parameters. In general, SAW devices can be fabricated on a piezoelectric substrate such as, for example quartz, lithium niobate, lithium tantalate, lanthanum gallium silicate and the like. Such SAW devices typically include one or more pairs of intertwined interdigital structures that are capable of converting applied electrical signals into electro-mechanical surface acoustic waves. Surface acoustic waves generated by applying the electrical signal on the inter-digital structure have propagation velocities that are sensitive to changes in stress and temperature of the substrate. Thus, all external parameters leading to a change in the stress and temperature of the SAW device can be detected. Such changes may be identified in terms of the shift of the resonance frequency associated with SAW resonators, or in terms of the delay time or phase shift of electrical signals emanating from SAW delay line components, by piezoelectric effect.
Real-time structural health monitoring of assets (SHMA) is a key strategy of industrial process control for condition-based maintenance (CBM) and thus, it can be employed as an intelligent alternative to present scheduled-based maintenance operations. The CBM approach can be employed to maximize the continuous operation time of running equipment and reduce maintenance costs to a minimum level. CBM can be preceded by a proper definition of normal operating conditions for the equipment as per its specification, as well as a deep understanding of failure mechanisms of the asset under consideration. As a result of these considerations, small sized, wireless and/or passive sensors can be employed for solving SHM requirements in order to constantly monitor the “pulse” of the equipment and provide an alert signal to an operator when a threshold value of a physical vital parameter is out of a specific range.
Along these same lines, moving mechanical parts are typically the weak point of many industrial or automotive components. The wear and tear experienced by such moving mechanical parts can generate changes in their ability to operate, particularly in terms of noise, excessive vibration, excessive heating, and fluid leak, which finally determine malfunction and overall failure. Furthermore, usage of such assets beyond their normal operating regime, without being detected in time can result in other components becoming defective and thus, a costly failure may result. The SHM of moving/rotating parts of such assets is complex as such an approach requires a wireless sensor to be located on or very close to the moving part in order to wirelessly communicate with an electronic reader placed in a static location with respect to the equipment to be monitored.
Based on the foregoing, it is believed that a need exists for an improved multi-measurand SAW-based micro-sensor apparatus and method for simultaneously monitoring parameters/conditions such as, for example, acceleration, vibration and temperature of particular assets in order to generate a warning signal to an operator regarding the measurands at a specified location. A need also exists for a wireless and/or wired SAW-based sensor apparatus capable of carrying out such features.